1. Field of the Invention
The present invention relates generally to seats and to the manufacture of seats, and more particularly, to a method and apparatus for making a seat including a seat cover bonded to a contoured foam substrate.
2. Discussion of the Related Art
Padded seat assemblies, and particularly padded seat assemblies for motorcycles and similar vehicles, are typically constructed using a foam substrate covered by it seat cover. The foam substrate is generally formed by expanding foam within a mold to the contoured shape of the finished seat assembly. The seat cover is secured tightly over the foam substrate so that it generally conforms to the contour of the foam substrate. The seat cover may be a cloth, leather, vinyl or any other similar material. A very stylish and popular seat assembly type is a bucket seat assembly having a concave seating surface. This seat assembly type presents some difficulty in manufacturing to ensure that the seat cover closely matches the concave seating surface.
In the past, buttons, stitching or similar fasteners were passed through the seat cover and the foam substrate to cause the seat cover to more closely conform to the concave contour of the foam substrate. This method of securing the seat cover has a number of disadvantages. For example, the seat cover may be locally weakened where the fastener passes through the seat cover. Also, the holes necessarily formed in the seat cover may allow moisture to seep into the foam substrate and/or moisture in the foam substrate to seep onto the seating surface. Finally, the fasteners may introduce wrinkles into the seat cover that may be aesthetically unappealing.
To provide a smooth surface finish to the seat assembly and to cause the seat cover to closely follow the contour of the foam substrate, it is now known to adhesively bond the seat cover to the foam substrate. Bonding the seat cover to the foam substrate ensures that the seat cover remains in close intimate contact with and conforms nearly identically to the contour of the foam substrate. Also, adhesively bonding the seat cover to the foam substrate advantageously eliminates the need for passing buttons or other fasteners through the seat cover for securing it closely to the foam substrate. This prevents tearing of the seat cover, simplifies the manufacturing process and overall provides a better looking more durable seat assembly.
It is generally known to use a heat source to heat and thus activate a layer of adhesive disposed between the foam substrate and the seat cover to adhesively bond the !;eat cover to the foam substrate. This process allows positioning of the seat cover over the foam substrate before activating the adhesive, and thus, allows accurate positioning of the seat cover before permanently bonding it to the foam substrate. For example, U.S. Pat. No. 5,407,510 discloses a method of making a seat where a foam substrate, clamped against a vacuum table, is urged along with a layer of adhesive and a seat cover against a heated fluidized bed that heats and activates the adhesive. Thereafter, the seat cushion is withdrawn from the fluidized bed. A vacuum may then be used to draw cool air through the seat cushion to cool it. The fluidized bed consists of beads of glass held captive by a flexible and permeable membrane cloth with heated air pumped through the glass beads to urge them upwardly against the membrane. The membrane is compliant so as to conform to the contour of the seat cushion.
In U.S. Pat. No. 5,176,777 a method of making a seat using a fluidized bed similar to that disclosed in the '510 patent is disclosed. Air is introduced into a chamber fluidizing glass beads contained within the chamber. A seat cover is placed on the top of a porous membrane that permits air flow through the membrane but retains the beads within the housing. A foam substrate is urged against the seat cover into the fluidized bed until the membrane of the fluidized bed conforms to the contours of the foam substrate. A heating coil is then activated to heat the air within the fluidized bed to, in turn, heat and activate an adhesive deposited between the seat cover and the foam substrate. No cooling is performed by the fluidized bed, and the process of activating the adhesive is rather slow.
U.S. Pat. No. 5,543,097 discloses a method of making a seat assembly where magnetic particles in the adhesive are inductively excited to generate heat to melt the adhesive. A vacuum is applied to urge the seat cover and adhesive sheet against a contoured cavity of a rigid mold bearing the general contour of the seat cushion desired to be produced. A pre-contoured foam substrate is thereafter placed into the mold against the adhesive layer. An electric current is introduced to a series of coils inside the mold to inductively heat the adhesive while a coolant flows through the coils to keep the foam substrate cool. During operation, a press urges the foam substrate against the adhesive and seat cover. This method may not provide uniform heating of the adhesive and subsequent uniform cooling of the adhesive. Additionally, the process requires rather expensive inductively activated adhesive.
It is also known to use steam as a heat source for heating and activating an adhesive layer between the foam substrate and the seat cover. An example of such a method is disclosed in U.S. Pat. No. 5,372,668 where cannulae or hollow needles pierce the foam substrate to introduce steam into the cushion relatively close to the adhesive between the foam substrate and seat cover. U.S. Pat. Nos. 5,372,667 and 5,286,325 disclose a method of making a seat assembly where the foam substrate is coated with an adhesive, and a press urges the foam substrate, adhesive and seat cover against a mold having holes in it. The holes allow steam to be introduced into the mold and to directly heat the adhesive. Thereafter, the seat assembly is transferred to a cooling mold to cool and set the adhesive. And, U.S. Pat. No. 5,232,543 discloses a method of making a seat assembly utilizing tubes with holes in the tubes to spray steam into the seat cover fabric to heat the adhesive. A vacuum source is turned on after steam has been introduced to evacuate the steam and any water that has condensed in the seat cover fabric. These methods introduce steam directly to the finished product. Steam condensing on the seat cover may damage the material while wetting of the foam substrate may require additional drying steps. Moreover, releasing steam directly into the working environment may potentially pose a worker safety concern.
U.S. Pat. No. 5,486,252 discloses a method of making a seat cushion using a flexible planar electric heating element made of silicone and heating coils that is placed between the cover and foam substrate to heat the adhesive. Thereafter, the heater is removed and pressure is applied to the seat cover and foam substrate to urge them together. Pressurized cooling air is then introduced into a porous fixture of a press that bears against the seat cover fabric to cool and set the adhesive.
While the use of adhesive bonding of the seat cover to the foam substrate has greatly improved seat assembly quality, the use of adhesives, and particularly heat activated adhesives, still pose a number of manufacturing problems. For example, a heat activated adhesive, such as a thermoplastic adhesive, does not gain strength until it is cooled significantly from the heated, activated state. Any movement of the seat assembly during this time can cause the seat cover to separate from the foam substrate resulting in a defective seat assembly. Defective seat assemblies must be rejected and either reworked or scrapped at considerable expense.
Moving the heated seat assembly from a heating fixture to a cooling fixture, in addition to adding to manufacturing complexity and cycle time, introduces an opportunity lo separate the seat cover from the foam substrate before cooling, and thus setting, the adhesive. Heating the adhesive prior to bringing the seat cover into contact with the foam substrate in a cooling fixture presents other problems. For example, it is difficult to uniformly control the temperature of the adhesive either on the surface of the seat cover or on the surface of the foam substrate. Moreover, it is a very difficult task to manipulate the seat cover relative to the foam substrate while the adhesive is tacky, i.e., activated. If the seat cover is not initially perfectly aligned with the foam substrate, subsequent attempts to align the seat cover are difficult and may result in a separation of the seat cover from the foam substrate. Seat assemblies with misaligned seat covers or improperly bonded seat covers are unacceptable.